Error detector for start-stop telegraph printers



May 23, 1950 J. c. WARWICK, JR

ERROR DETECTOR F'OR START STOP TELEGRAPH PRINTERS 2 Sheets-Sheet 1 Filed March 6, 1948 K Rm mA wW Lua 5 E M A J ,JR [Mick May 23, 1950 J. c. WARWICK, JR 2,508,554

ERROR DETECTOR EoR START sToP TELEGRAPE PRINTERS Filed March 6, 1948 2 Sheets-Sheet 2 INVENTOR ATTORNEY JA ES C. WARWICK,JR. BY -/a,

atented May 23,

ERROR DETECTOR FOR START-STOP TELEGRAPH PRINTERS James C. Warwick, Jr., Bcechhurst, N.'Y., assignor to Radio Corporation of America, a corporation oi' Delaware Application March 6, 1948, Serial No. 13,444 1o claims. (cuis-69) l This invention relates to error detectors for start-stop telegraph printers. In my United States Patent No. 2,353,327. granted July 11, 1944, I disclose certain types oi' error detectors for start-stop printers, in which the error mechanism is controlled by the pull bars of the printer. In this application an improved type of error detector is disclosed in which the error mechanism is independent of the pull bars.

An object of the invention is to provide an error indicator controlled directly by the signal magnet in a start-stop printer.

Another object of the invention is to provide an improved step-by-step error mechanism operated by the selector levers of the start-stop printer under the control of the telegraph signal magnet.

Other objects will appear in the following deseription, reference being had to the drawings, in which:

Fig. l is a plan view of the error detector mechanism and certain associated operating parts;

Fig. 2 is an elevational view partly in section, looking in the direction of the arrows of the plane 2-2 of Fig. 1;

Fig. 3 is a section, partly in elevation, taken on line 3-3 of Fig. 1; and

, Fig. 4 is a graphical representation of a` seven I.

unit code combination for the letter A.

In start-stop telegraph printer systems as distinguished from the synchronous, type of printing systems, the receiving cams are all started in unison with the transmitting cams by interruption of the signal current at the transmitter. This is the start impulse of a code sig- ,nal combination. The receiving cams are rotated slightly faster than the transmitting cams and automatically stop at the completion of a code signal combination so as to be in Ya posi- 'cams there will be only, and always, three mark or current impulses among the seven character code signals. Hence, if more or less than three mark impulses are received, it is the result of an error and my improvement provides means for indicatingA such error by having an error character printed in place of the intended character.

Referring now to Fig. 1 of the drawings, when no signals are being sent, the line magnet I is energized and the armature 'I is held in the po- Y sition indicated. At the start of each code combination the signal current is interrupted and the magnet I de-energized. This throws the clutch release 2A, and the cam member 2 begins rotating. If a signal is sent out to give a mark or current impulse, the magnet I is energized again as the cam I approaches the cam follower 6 of the first selector lever 3, the remaining levers being hidden from view. The armature I is moved to the closed position shown; the armature extension arm I0 and the sword I4 engage each other at prong I2 and side projection 23 as the lever 3 turns counter-clockwise when follower 6 rides over the cam. This shifts the selector T lever end I9 to the right for a mark signal. The above mentioned operating parts of the cam and selector mechanism are of the wellknown start-stop teletype printer. These are essentially the same as those illustrated in my United States Patent No. 2,353,327-,` and are outlined here only to describe their relationship to the device of this invention.

The receiving cam member 2 has eight cams (I to VIII) substantially uniformly spaced at diierent levels around the periphery for operating the seven selector levers and also the print bail cam clutch release 2B. Only one selector lever is shown at 3 in Fig. 1, the others being omitted for clarity of illustration. The clutch and other parts are not shown, as this is not required for an understanding of my improvement. The seven selector levers are spaced, stacked one above another and pivoted on a common rod 4 as indicated by Fig. 3. Seven individual springs 5 tend to rotate their respective selector levers 3 in a clockwise direction, indicated by the arrow in Fig. 1, and also serve to keep the cam followers 6 against their individual cams I, II, III, IV, V, VI or VII. The cam member clutch release 2A and the print bail cam clutch release 2B also have individual springs (not shown). The signal magnet I has its armature 1 pivoted at 8 for limited move.- ment in a counter-clockwise direction upon energization of the magnet, which is indicated in Fig.

spectively, of sword 14 at each sideof theend of the selector levers 3.-` The prongs ll andy l2 extend downward at right angles to the plane of the drawing. f

The lower end of each selector lever 3 hasa ball and socket engagement with its individual SWOrd I4, Which has a pointed end adapted to engage either the arms l5 or I6 of a'small Telever. I1

respective cams I, II, I'II, IV, or Vlrwl'ieri the cam member2 rotates.'

When the magnet'iis energized, asv Ona mark impulse, the sword lmoveswith selector leverlS and the side projection 23 engages prong l2 as Ytha-cam follower. 6 rides Vover itsindividualv cam point and this movement throws the blade vI4, to the left, as shown in Fig. l. Then, as the cam piolnt moves past the camfollower, spring; ro-k tates the lever and'forcesk the pointof the sword -liagainst the arm l5.ofthe.r T-lever. andsets its individual code bar 2| for movementto the righti If the signal magnet I had been defenergized; thatis, if a space impulse hadbeenreceived, prong ll. would have been in pixsition to engage projection 22 on the swordas the follower moved o ver the cam point and Atherblade I4 .would then have been positioned to the right inFig.' 1. The movement of the selector leverunder action of spring 5 then would have-,setthe codebarfZlf for movement to the left. Stop pins Ma. only prevent an Vexcess movement ofblade .l4. Thev foregoing description discloses the well-knownl selector mechanism of the teletype printer for sevenunit code signals. i v

.Inmy improved invention'an extension arm 24 isY added to each one ofthe seven selector. levers 3, with a projection or lug 25 at the free end ofthe extension arm. `A slide bar 2d has a slot 2lV slidone Yend of slide bari. V This slide .bar-1 26 also into position to engage the lugs 25 on the selector lever extensions. As the various selector levers 3 are turned counter-clockwise by their individual cams, the slide bar 26 will be moved rearward, causing pawl 30 to engage and turn the ratchet wheel 32 one step for each cam passed over )while Ythe magnet is energized due to mark or vcurrent impulses.Y

Ratchet wheel 32 has a second set of teeth 39 One end .the secondportion of wheel 32 under stress of spring 43. The other endV of pawl '45 engages a pin 4d on the end of a release lever 45 iixed to shaft 4-fwhich isr of sufficient length to extend below base'29. The other or cam end 46 of lever 45.is, ;adapted to,be engaged once each complete revolution of the cam member 2 by cam 48 and when so engaged, the engaging end 42 of stop pawl .45 is moved out of engagement with the second set of teeth A3 Bf; and then a helically wound spring 5G which surrounds bearing. 33a..v (Figs 2), rotates the ,ratchetwheel 32 andialower. rotor member 50a clockwise.y untilthe roller engaging bar 5i (located so as .to slide in a. slotas shown in Fig. 2) Vis brought into. engagement with stop pin 5,2. This occurs immediately aitercamtip on camv member-2; has tripped the., errorbar Y blocking mechanism?. by. rotatingmshaft.. 4l and thus moving a lever 49 fixed to thelowenende oi the shaft. A spring: 53B;maintains-thefrollenengaging bar 5| in its vnormal position.

A pivoted lever 534 is provided adjacentan'erroi:

'pull bar 54 adapted to fallinto theslots 55 in each i slidably positioned in a standard 55 towards ,has a'pawl'r pivoted at the Yother` end at 3|, V'so Vthat theupawl canengage the teeth of-ratchet whee1'32 on shaft 33 journaled in' bearing 33a fastened to base plate' 29.y A spring3r4- fastened' Vto the end of the pawl maintains the'pawlagainst apin 36 fastened to theslide 26; ofA spring 34 is fastened to aflnger-on slide bar 26. A second spring SGA isLfastenedat one` end vto the finger of the`slidebar 26 and urges the pawl and slide bar towards their foremost position, as shown in Figl. The other end of spring SAis fastened'to a pin on base 29;

armaturel ink 31 is pivoted atone end Vto Vthe armature extension l0 and at the othervendv The otherl end -ing lip; 58 adaptedto engage' a. catch 5e on a latch 6d pivotedatl inthe/standard 5mt-mounted undervba'se plate 291. Theflatcht. has afdownA wardly Vprojecting end t2.V *Spr-ing;4V 63f, With- Aits ends fastened-to thelatch llaid totheL -base 1 Y plate l25J, tends to rotate thelatchcounter-cldcktothe slide 26. This linkV maintains the pavvl.E 30

in position for engagementwith' a-wiirst set-of teeth on one portion of Vratchet-wheel 32 when the magnet l is energized and removes it there- Y from by rotating bar264 around the 'pivot-'rodf 28 lwhen the magnet I isde-energized. When the Y l'magnet' is energized, the downwardyext'ending bar 38 ononeend portionofthe slide y26 iszmoved wise. Y

' VVThe'lower rotor member 50ct-has` a slot ih which the rollerengaging bar 5ft isadlaptedito Vmove'on bearingvsliA so as to engage5- the lever? 533 at projection (54` after the..` ratchet wheel-.32h25 V'been stepped forward threeA teeth, butcwillifnot beso adapted-when-.it hasbeen steppedi-forwa-rd more or less than threelteethrbyactionoffpawl 30. Y

Y The well-known operating or print .bailai 'tliuof :the usual' start-.stopV printer has; a lipI 'l2 .holding Y Vthe pull bars Vout of theislots ini the.codebars, :which lip is shaped tol engagethe :hooks 'iiofrthe .pull bars upon `its upward movement '-.wl'ieni the pullibars fall into the aligned slots: .-in-A the Vc ode bars. Y' Before thev bail- 1 I freachesf-its vupp erm'o'st position-1in this movement (but afite'r.- it'ghas iengaged the:V selected pulls bar-2 for: anx erroneo;

character). the end 62 of the latch 60 is engaged and the latch is rotated clockwise to free the lip 58 on lever 53 of its engagement with the catch 59, if it has been previously moved into engaging position. An extension mounted on the rear of bail 1l is so positioned as to engage arm 16 of link 61 and rotate it clockwiseas bail 1| moves upward. This movement engagescatch 11 in second latch 66 against the compression of spring 80 and brings down a ram 68 and a large 4roller 10 to their low position. Roller 10 is held to roll in its track 13 by spring 8|.

A Ysmall roller 19 is positioned on extension 15 to engage spring-loading lever 18 as bail 1| moves downward. This engagement rotates lever 18 counterclockwise, tensioning spring 69 against ram 68. An arm 49 is fixed to shaft 41 and is positioned to depress latch 66 when arm 46 is moved counterclockwise by cam 48 on cam member 2.

The operation of the improved error detector of this invention will now be described.

Suppose signals of the seven unit equal-length code are being used, as disclosed in my United States Patent 2,353,327, supra: With this code, each character always comprises three mark impulses and four space impulses. Differentiation between characters is obtained by different time positions of the mark in the cycle.

Let it be supposed, for example, thatthe letter A is being received. This letter consists of a.

v32 and its attached rotor member 50a one step counter-clockwise. Stop pawl 40 will engage one of the second set of teeth 39 and hold this advance of member 50a. f

It will be understood that the movement of the selector lever 3 through the sword |4 and T-lever l5 will set the rst code bar 2| for movement to the right.

The second signal impulse for letter A. isl a-l space, and magnet I will not be energized. Therefore, as the cam follower 6 rides over cam point II, the lug on the selector lever eX- tension 24 will not engage the bar 38 on the slide 26. of the slide 26 and, furthermore, the pawl v3|] will not be in engagement with the lower rotor ratchet wheel 32. Thus, the member 59a will not be advanced for this second unit of the character beingV transmitted. It will be understood' that a selector lever, sword and T-lever will set the second code bar 2| for movement to the left.

The mark impulse of the third unit of the letter A will step the member 50a forward a second notch, in the way already described, and will set the third code bar for movement to the right.

The mark impulse of the fourth unit will energize the signal magnet and cause the member 50a to be stepped forward a third notch. -This will move the roller engaging bar 5| in line with projection 64 on error lever 53, and will set :the fourth code bar for movement to the right.

,When the fifth, sixth and seventh units of Therefore there will be no movement `their correct mark and space positions.

'the letter A are received, there will be no move ment of the member a because these units are space impulses and the magnet will not be energized. The fifth, sixth and seventh code bars will be set for movement to the left.

Immediately following the start of the seventh selector cam operation, cam projection 48 starts to move release lever 46 counter-clockwise, which in turn moves the lower arm 49 through shaft 41. This movement depresses latch 66, releasing link 61 so that ram 68 is shot upward by the tension of spring 69. The roller 10 on the vend of ram 68 is driven upward along its track 13 and against the sloped end of roller engaging bar 5| which was rotated to this engaging posi'- tion by the third marking impulse of the letter A. Roller engaging bar 5I, by the action of roller 10, is pushed forward through member 50a against surface 64 on the error lever`53, and moves lever 53 counter-clockwise so that its lip 58 latches in catch 59 of latch 66. At the same time spring 50B is compressed. The latching of lever 53 blocks the entry of the error pull bar 54 into the aligned slot 55.

While lever 53 is being latched, a further counterclockwise movement of release arm 46 causes pin 44 through arm 45 to rotate stop pawl 46 clockwise, lifting its end 42 clear of holding the second set of teeth 39 on ratchet 32. Thus freed, the helically wound spring 50 will return ratchet wheel 32 and member 56a clockwise until bar 5I stops against the stop pin 52.

.Seven units of the signal code having been received, no error resulted in the transmission and the code bars 2| are now set to move to This will align a clear slot in all the code bars adjacent the pull bar for the letter A (not shown), and this pull bar will move forward into its cleared slot in the well known way and will be elevated by the upwardly moving bail 1| to print the character A, after cam VIII has tripped the clutch release 2B to operate the print bail (not shown) cam of the printer. As the bail 1| moves upward, it cannot engage the hook 14 on error pull bar 54 because this pull bar has been prevented from entering the wide slot 55 in each code bar by lever 53 and this hook 14 will be outy of the path of the lip 12. After the bail Il has engaged the pull bar for letter A, it will then engage the end 62 of the latch 69 and rotate it clockwise. This will release the lever lip 58 from the catch 59 and the spring 51 will return the lever to its unlatched position (not shown). Thus, the letter A has been printed and the error indication was not made or printed because the error pull bar 54 was blocked out of the slot 55.

As roller engaging bar 5| is being returned to its'stop pin 52, cam VIII sets the printing opera- -tion in motion. As stated above, the bail 'H moves upward. The bail extension 15 in turn raises arm 16 of link 61 until catch 11 moves behind latch 66, thus withdrawing roller 1D from its'upper and drawing it down to its lower position. Here it is held until the next selection has been made by cam member 2, and cam 48 again causes roller 10 to be released and shot upward. Spring-loading lever 18 follows extension. 15 in its upward travel, thus permitting link 61 to be latched under relatively light spring tension. On its return to its lower position, roller 19 depresses lever 18, thus tensioning spring 69 in readiness for the next release of link 61.

lacter representative of `a predetermined number of selected elements in received code combination, a plurality of slotted code bars linked to said message selector levers, a magnet and an armature coupled to actuate said selector levers, an error selector leverv positioned to engage a slot in said slotted code bars, an armature link, a slide bar linked to said armature by said link, a pivot rod forv pivoting said slide bar, a ratchet wheel, means on said ratchet Wheel for counting the number of mark and space units of a signal, and means including said armature link for rotating said slide bar around said pivot rod, and. to actuate the Iratchet wheel to a 4position lsuch as to have said error bar retained in the 'slot of said code bar to actuate andi'pint the character indicating a l tector comprising a plurality of message selector levers, a plurality of slotted code bars linked to said message selector levers, a plurality of message type levers adapted to be selected by said selector levers for printing a character representative of a predetermined number of selected elements in a received code combination, an error type lever for printing a character to indicate any departure from the predetermined elements vin the received code combination, means controlled by signal current for selectively moving said message selector levers to position said slotted code bars with aligned slots adjacent a selected one of said message type levers, an extension arm on said message selector levers, a slide bar positioned to engage said extension arms and to be actuated by said means controlled by the signal current, a pawl secured to said slide bar, a ratchet member having a plurality of teeth, positioned to be engaged by said pawl, an engaging bar linked to said ratchet member, a roller member, means including said ratchet member to move said engaging bar member only when said ratchet has been stepped in accordance with said predetermined number of selected elements to disengage said error type lever when the predetermined number of selected elements in the received code combination are properly received and when the code combination is not properly received to position said roller out of line with said engaging bar thus causing the error type lever to print the character indicating a departure from. the predetermined number of elements in the received code combination.

7. A telegraph printer having an error detector comprising a plurality of message selector levers, a plurality of message type levers adapted to be selected by said selector levers for printing a, character representative of a predetermined number of selected elements in a received code combination, a plurality of slotted code bars linked to said message selector levers, an error type lever for printing a character to indicate any departure from the predetermined elements in the received code combination, means controlled by signal current for selectively moving said message selector levers to position said slotted code bars adjacent a selected one of said message type levers, means to retain said error type lever in an engaging position in a wide slot located in said slotted code bars, an extension arm on said message selector levers,

, a slide bar positioned to be actuated by said exing bar linked to said ratchet, a roller member, means including said ratchet to position said engaging bar in line with said roller member on receipt of the predetermined number of selected elements to move said error type lever out of its engaging position in said wide slot of said slotted code bar, thus permitting the selected one of said message type levers to print, and to position said engaging bar out of .line with said roller toengage said error type lever in the Wide slot in said code bars causing. the error type lever to print the character indicating a departure fromthe predetermined number of elements in the received code combination. .i Y

L8. A telegraphvprinterbf the, start-stop type particularly adapted for a fixed length code each character of which is represented by signals having va iixed number of signal elements. of one nature. and. having'error detector means, comprising a plurality rif/message selector levers,a plurality of slottedI code barslinked tosaid message selector levers, .a pluralityfof message type levers adapted to be selected by said selector levers for printing a4 character representative of the elements in the received code combination, an error type lever for printing a character to indicate any departure from the predetermined fixed number of elements of one nature inthe received code combination, means controlledby signal current for selectively ,moving said message selector levers to position said code bars to align the slots adjacent the selected one of said message type levers, an extension arm on each one of said message selector levers, a slide bar positioned to be actuated by said extension arms, a ratchet having a plurality of teeth, a pawl secured to said slide bar and positioned so as to engage the teeth on said ratchet, an engaging bar linked to said ratchet, a roller member, means including said ratchet to position said engaging bar in line with said roller member to disengage said error type lever when the predetermined number of selected code elements occur to permit the selected one oi' said message type levers to print, and to position said engaging bar out of line with said roller to engage said error type lever to print the character indicating a departure from the predetermined fixed number of elements of one nature in the received code combination.

9. A telegraph printer of the start-stop type particularly adapted for use with seven element code each character of Which is represented by a signal having three marking and four spacing elements and having error detector means, comprising a plurality of message selector levers, a plurality of slotted code bars linked to said message selector levers, a plurality of message type levers adapted to be selected by said selector levers for printing of a character representative of a predetermined number of selecting elements in a received code combination, an error type lever for printing a character to indicate any departure from the predetermined number of elements in the received code combination, means controlled by signal current for selectively moving said message selector levers to position said code bars to align the slots adjacent the selected one of said message type levers, an extension arm on each one of said message selector levers, a slide bar positioned to be actuated by said extension arms, a ratchet wheel having a plurality of teeth, a pawl secured to said slide bar and positioned so as to engage the teeth on said ratchet Wheel, a pivoted lever, an error pull bar positioned to be actuated by said pivoted lever, an engaging bar linked to 

